Context-dependent transcription factors play a critical role in defining which genes are regulated during development and disease, allowing the same factors to play different roles in different cells. The C. elegans embryo is an deal system for a comprehensive study of the role of lineage history in the context-dependent regulation of cell fate because of its invariant lineage and powerful experimental tools. We recently developed automated lineage tracing and expression mapping methods for C. elegans embryogenesis and measured the expression of over 127 fluorescent reporters for transcription factor (TF) expression in every cell of developing embryos. From this dataset, we identified over 30 TFs whose expression correlates directly with both lineage identity and Wnt signaling but not with terminal fate. In Aim 1, we will apply our lineage tracing methods to elucidate how context factors determine differential cellular respones to Wnt signaling, a key cell fate regulator and driver of oncogenesis. We will do this by assaying binding of the Wnt effector POP-1 to candidate targets, genome-wide mapping of POP-1 binding and detailed cis-regulatory analysis. In Aim 2, we will determine the function of TFs with lineage-specific expression by high-resolution phenotyping and genome-wide expression profiling of mutants. These studies will define mechanisms by which lineage identity is translated into cell fate and shed light on context-dependent differences in TF and Wnt targets in C. elegans and other organisms.